What is the logic to having an axis labeled Z and also having Z refer to distance from the camera?
Quoting from iKlsR's answer:


  Blender uses the right hand coordinate system with the Z axis pointing
  upwards. This is common with the coordinate systems used by most
  common 3D CAD packages.


However, it's also a standard to use Y up for images (with Z as depth).

To help with getting used to it, you could try a couple things:


Imagine you are looking at the image editor top down instead of from the side.
Think in terms of the camera's local coordinates (the local Z is always out the front)